Communication and radio guidance system



A n E m A R O E D M. E

COMMUNICATION AND RADIO GUIDANCE SYSTEM ll Sheets-Sheet 1 original Filed April 29, 1944 INVENToRs EDMOND M. DELPH//VE PZ/ E HDF/*76 Arma/vn' L A T E E m A R O L E D M. E

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COMMUNICATION AND RADIO GUIDANCE SYSTEM 1l Sheets-Sheet Original Filed April 29, 1944 EDMOND De@ Z6, 1950 E. M. DELORAINE ETAL. 2,535,048

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COMMUNICATION AND RADIO GUIDANCE SYSTEM Original Filed April 29, 1944 ll Sheets-Sheet 6 M W446i cmu/rs 130 122 #5f/v5.5)

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COMMUNICATION AND RADIO GUIDANCE SYSTEM Original Filed April 29, 1944 ll Sheecs-Sheeil 7 @H057 IND/CH T/N INVENTORS [F0/wam@ M. 25mm/Aff PAUL /R A04/W6 ATTORNEY E. M. DELORAINE ET AL.

COMMUNICATION AND RADIO GUIDANCE SYSTEM Original Filed April 29, 1944 1l Sheets-Sheet 8 INVENTORS @Mo/v0 M naam/wf Dec. 26, 1950 E. M. DELQRAINE ErAx. 2,535,048

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COMMUNICATION AND RADIO GUIDANCE SYSTEM Original Filed April 29, 1944 ll Sheets-Sheet 11 wfsraww 56? Riff-ame k/ 386 Y i I i @75 ATTaRA/EY Patented Dec. 26, 1950 t COMMUNICATION AND RADIO GUIDANCE SYSTEM Edmond M. Deloraine, Paris, France, and Paul R. Adams. Cranford, N. J., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Original application April 29, 1944, Serial No.

533,322. 4Divided and this application Decembet 15, 1945, Serial No. 635,340

s claims. l

'I'his invention relates to airplane guiding and tramo control systems and pertains more particularly to radio systems for guiding airplanes along established routes and in approaching,

landin an takin ofi' from airflel s; thi ein a diviondof cui. copendmg apmcatir? foi 5 a. Several guiding and other functions are com- Trame Controi systems". serieu No. 533,322, billed with a Orrespmding Saving i equip died Aprn 29, 1944 which issued september 12, ment and frequencies- 1950 as Patent No 2,521,697 b. Several functions are carried out successively One of the objects of our invention is topro- 10 in ne in order tio share he uns; among a' vide a system of aids to navigation and tramo numdr of Success ve func ons W h a' come' control for use in extended operation of aircraft son ng saving tn equipment and frequen' so as to permit regular operation by a standardc es' ized procedure under all weather conditions. In accordance with the present invention, air- Certain other objects of the invention involved'in lli Dort tram Control of planes prior to landing this system include the provision of methods and is effected by giving the airplanes such informameans to meet the following requirements: tion that they can follow circular paths centered on the airport. The radio ranges which define a' The use of a minimum amount of radio equip' the airways leading to the airport are connected ment on the airplane' 20 with the circles by tangential paths or branches b- The use 0f a minimum number 0f frequency which are used for arrival and departure of the channelsairplanes. The circles are characterized by spec. Simplicity of operation and indication. -cific radii and altitudes and any number of such d- An Operating DI'OCedUIe remaining substancircles may readily be provided. Ordinarily only tiaIly the/anle in all Weather ConditiOnS- 26 one circle for agiven altitude will be required but e. The 118 0f Speech ommnncation to'give basic more than one circle could be provided if desired.

instructions from the ground to the airplane. Means is provided for advising the airplanes foland the provision 0f instruments 0n the airlowing these circles of their angular position with Plane Suitable for carrying out these instrucrespect to the center or what is equivalent, their tions. an position along the circular path in which they f. The provision of information on the ground are supposed to be flying.

suillcient to supervise all planes' movements. The information required on the ground at the to check that they are correct or to issue supalrport traiic control station is essentially the plementary instructions. following: g gris fasiugstg'gmdual introduction t 3 a. Knowiedge ofthe position, altitude and identification of all planes following the air route The growth of military or civil aviation as a determined by the radio ranges. transportation service has been marked so far b. Knowledge of the position, altitude and idenby a number of progressive steps in the solution o tiflcation of all planes following the circular of a number of individual problems as the i'ull paths around the airport (before entering a importance ofeach became apparent. runway localizer beam for landing or after While step-by-step progress in the minimizaleaving a take-off runway). tion of natural and artificial limitations had the c. Ability to check all movements of planes. advantage. of presenting the problems succes 1l For safe guidance and control of aircraft along sively, it resulted in a decided disadvantage in i ti l that these individual solutions of problems have a rways' the fonpwmg radio informa on and fa' ilities are required by each airplane: resulted in the development of equipments that c are largely unrelated and independent, each rea. An indication of left-right location i. e., quiring its own frequency and antenna and in 50 whether right or left of the airway (generally total adding considerablly to the airplane load known as the radio range facility). and drag thus involving a cost and maintenance b. An indication of left-rightI altitude i. e., DIObleln 0f Some importance. whether headed left or right of the next sta- In order to obviate many of the dilliculties of tion ahead on the airway (generally known asA prior systems and to simplify the apparatus rcu quired on the airplane, while at the same time oerlng other advantages, a further object of our invention is to provide a universal system" involving the following principles:

the homing facility).

c. A knowledge of altitude above` ground (generally known as the terrain clearance facility).

d. A knowledge of position along the airway (hereinafter called-the self-distance facility).

e. A knowledge of nearby aircraft (generally known as the anti-collision facility).

f. One or more channels for short range twoway telephone communication with airplanes nearby.

g. A larger number of channels for longer range two-way telephone communication with the distant airbases from any point on the airway.

The airways control center such as a terminal airport requires the following information facili ties:

The number of radio frequency bands needed for providing even the present 200 commercial civilian airlines with present existing facilities would be substantially greater than the number of bands now allocated for all civilian aeronautical uses; and with increasing numbers of aircraft as expected the shortage of bands will become rapidly more acute. The difficulty of obtaining new allocations of frequencies, moreover, can be expected to be extremely great if the bands requested lie in the L. F. (low frequency), M. F. (medium frequency) or H. F. (high frequency) regions hereafter referred to as the longer range wavelengths, such dimculty being substantially less if the bands requested lie in the V. H. F. (very high frequency), U. H. F. (ultra high frequency) or S. H. F. (super high frequency) regions hereafter referred to as the optical range wavelengths. It is, thereafter, necessary at the outset to consider how many of the desired facilities can be satisfactorily taken care of by optical range radiations and how many really require the longer range wavelengths.

It is at once apparent that the terrain clearance, self-distance and anti-collision facilities above listed as c, d and e would normally be performed with the optical range wavelengths. It is also fairly clear that the plane-to-plane telephone communication above listed as f could be taken care of by optical range radiations. In addition the radio range and homing facilities above listed as a and b can be performed with optical range wavelengths if one is willing to increase the number of range stations by a factor of about two to one.

The equipments required on the ground are approximately as follows:

1. A number of radio range transmitters suitj maintain optical line of sight with any airplane flying along any of the airways.

A sufficient number of communication channels to interconnect all the radio-telephone stations mentioned in 3 above, with the night control centers.

A number of radar equipments spaced along the airway at suitable intervals to maintain almost optical line of sight with any airplane flying along the airway.

. A suflicient number of communication channels to interconnect the radar equipments mentioned in 5 above, with the flight control center.

A number ofl base-to-base telephone, telegraph and facsimile circuits between the airbases at the ends of the airway.

In the system of the present invention, it is further contemplated that the combination stations atl which all the required communication and navigation facilities are to be concentrated should be spaced somewhat closer than in the past (which permits the use of smaller power not only at these stations but also in the airplane transmitters) and should each be provided with a tower of moderate height. By such arrangement, it is possible to provide an optical line of sight between each tower and the next one; and the proposed system takes advantage of this fact to provide the required group of communication channels between airports by means of a series of 'multi-channel U. H. F. or S. H. F. radio links between successive towers. A wide-band repeater equipment is provided in each tower, so that the successive radio links are joined together into a chain which forms an artery of communication, extending between airports and capable of carrying a number of communication channels.

The relay stations along the airway must be at such distances apart that there is an optical path between the tops oi' the successive towers installed at these stations. In order to limit the towers to less than 100 feet, the spacing will be 20 miles approximately in flat country and usually larger in regions of irregular level.

Each tower carries four antennas for radiating and receiving narrow beamed micro-wave links in both directions and also a two-way U. H. F. broad band repeater to join these links into a continuous chain. Such chain handles a ymulti-channel communication system between the distanct airbases. Such communication system carries all the base-to-base traine including facsimile transmission service.

This multi-channel system may, in addition, have outbranching channel equipment for branching a few communication channels out from the artery at each tower or relay station and also inbranching channel equipment.

For example, a chain of towers extends east and west between two airbases. The western airbase may be referred to as the master base which primarily controls the facilities. Three channels from the eastbound artery from the master base may be branched out at each tower and five channels may be branched in from each tower into the westbound artery for reception at the master base. Of these three outbranching channels, two will be the same channels at all towers. while four of the ilve inbranching channels will likewise be the same channels at all towers, these being used to handle a quasi-radar service and synchronize the transmissions of the radio range facilities as more fully explainedk hereinafter.

air route having twenty to thirty towers.

assuma The remaining channel which is branched out at each tower as well as the remaining channel which is branched into the artery at each tower may be connected respectively to speech modulate a fixed-tuned low power V. H. F. radiotelephone transmitter and to receive speech from a fixed-tuned V. H. F. radio-telephone receiver for communication with airplanes near such tower. The two channels which are thus branched in and out at any given tower for twoway plane-to-base telephony will be diiferent channels from those similarly used at the adjacent towers. in order that a number of diil'erent pairs of channels will be available along the airway for simultaneous speech between the western ...base and a number4 of different `airplanes. The

channels used for such plane-to-base telephony may be repeated every few towers, however, so as to require only six to twelve eastbound and six to twelve westbound channls even for a long The V. H. F. radio frequencies used to carry the communications between the towers and the airplanes may also be repeated every few towers so that the airplanes V. H. F. radio-telephone equipments need only be capable of s;1ecting five or six different pairs of frequencies while yet permitting six to twelve simultaneous conversations depending on the number of channels. Many different allocations of channels and frequencies may be made in accordance with operating requirements, one or two typical arrangements being given by way of example in the more detailed description which follows.

As many channels as required canthus be provided for plane-to-ground use over long distances without requiring any frequencies other than ve or six V. H. F. speech bandsused in the airplane radio-telephone equipment and the two wide bands used for the chain of tower-to-tower links. It is especially to be noted that long range planeto-base telephone is thereby accomplished without the use of a single one of the scarce long range wavelengths below 30 mc.

One channel of the airplane V. H. F.1equipment can be reserved for direct communication with airplanes nearby. If communication is desired between planes too far apart for direct interworking, such communication can be carried on through the chain of towers in the same manner as a plane-to-base communication.

Heretofore desired information, whether readvantage of reduction in the number, weight and complexity of equipments and antennae and the reduction in the number of frequencies required is brought about by means of pulse modulation utilizing pulses of various types and characteristics. In order to combine the advantages of pulse operation with the benefits of conventional continuous wave (C. W.) operation some of the signals may be short pulse modulated car- .by other airplanes.

f 8 riers of V2 microsecond duration, more or less. which would be handled i'n accordance with pulse technique. while certain other signals could be much longer, and, in fact, may actually comprise brief signal trains of carrier waves modulated'with tone modulations which may be separated by the conventional heterodyning and nltering techniques used for C. W. transmission. While the use of short duration pulses results in a wider frequency band than ordinary C. W. transmission, if the number of channels required is taken into consideration, as well as the selectivity and frequency stability attainable in practice, the total frequency band required with the nzw system of our invention is much less than would result from the use of C.V W. methods.

Since the control of transmission is eecterl from the ground at the airport, it is possible to synchronize the various transmissions in such a way that the pulses and short trains of signals corresponding to the various services will be sent in sequence, and to leave in between pulses and signal trains enough time interval to take care of the effects of the different locations of equipments, and the diilerent locations of incoming and outgoing airplanes with respect to the same.

All of the pulses and signalling trains which are radiated from the various transmitters on the ground may be, in accordance with our invention, received by one antenna and one broad band receiver equipped with one or two antennas on each plane. The various types of signals used for dinerent services are separated by pulse separation techniques and by tone separation techniques, such separation being performed after the signals have been received and detected in the common receiver to yield the pulses or trains of tones.

Some transmission must take place from the airplane, for example, to determine the distance of the plane from the ground or from a repeater. In this case, it is not possible readily to synchronize the pulses sent by one plane with respect to the pulses sent by other planes. In the following description an explanation is given of how three sets of pulses may be sent from each airplane, one of these sets uses pulses of, for example, 1/2 microsecond duration transmitted at suiilciently long intervals so that their transmission times occupy only V2 of one percent of a given time interval. The other two sets of pulses transmitted from the planes are transmitted at still lower rates so as to occupy, for example. less than lo of one per cent of said given time interval, thus the percentage of pulses which overlap each other is small enough to avoid difficulties.

In the case of certain services, e. g. determination in an airplane of its own distance from the ground or from a repeater, it is necessary to distinguish between the reflected or repeated pulses originated'by the given airplane and other similar reflected or repeated pulses originated By using widely spaced pulses and permitting their repetition rates to vary in random manner within certain limits, it is readily possible to recognize the desired received pulses by the fact that their timing corresponds exactly to the timing of the pulses previously transmitted by the given plane.

From the foregoing introductory description and the following detailed description, it will be clear that our invention shows how to handle, at a given airport on a time basis and on one single nground frequency. the following 1. A number oi' radio ranges in .the same area converging toward the same airport. 2. A number of localizers simultaneously in use at the same airport.

. A corresponding number of glide paths simultaneously in use at the same airport.

A high speed 'rotary beacon radiating special azimuth signals successively in diilerent directions so as to enable any airplane to determine its azimuth in respect to the center of the airport.

. Range transmitters or beacons spaced -at desired intervals along the airways.

6. A forward scanning radio compass on the plane receiving the signals from any selected one of the localizer or range transmitters on the ground.

Assume, for example, with regard to items 1, 2 and 3 above, that there are four ranges, three localizers and three glide paths in use at once around one airport. Each of these determines an equi-signal path by means of two tone modulated carrier waves substantially as in the existing types of equipment. The two modulation tones used for any one of the equipments will be of the order of hundreds of kilocycles, however, instead of ninety and one hundred and :fiftycycles (so as to reduce the weight of the receiver iilter) and will be diierent from the tones" used in the other equipments. Thus. for ten equipments simultaneously in use twenty different modulating tones" would be used. The radiations, moreover, are intermittent and are timed so as not to overlap, thus avoiding interferences.

With regard to item 4 above, the beacon is generally similar to known types of omnidirectional beacons, but rotates at high speed so as to give substantially continuous indications. The rotating beam of this beacon is characterized by a null-and-maxirnum type of pattern essentially similar to an equi-signal pattern but produced by transmitting two kinds of pulses in immediate succession, one kind [of pulse being transmitted with a pattern which has a null along the axis of desired reception while the other pulse is transmitted according to a pattern which has a maximum along this axis. Thus, reception of the second type of signal without the iirst indicates that the airplane in question is aligned with the axis.

One can also transmit on one single airplane frequency (preferably higher than the ground frequency) a series of pulses generated on each airplane which will be used as follows:

l. To measure the terrain clearance by measuring the time between the transmission of these pulses and the reception of the same pulses reflected from the earth.

2. To determine the distance of the airplane from the center of the airport and/or from towers along the airway by measuring on each airplane the time interval between the transmitted pulses and the pulses retransmitted from a repeater at the airport or tower, as the case may be. This repeater will receive pulses at the airplane frequency, but will retransmit them at the ground frequency.

3. To show directly the position of the airplane with relation to a map of an airport and surrounding territory by combining the distance indication and azimuth indication above mentioned in a suitable polar coordinate indicator. Such an arrangement provides an accurate control o! the ilight patterns between the radio ranges and the localizer paths. the desired paths, the desired ight patterns being merely printed on the map upon which the position of the airplane is projected.

4. The same method enables the airplane to determine its distance from the end oi' the runway on following the localizer, thus replacing the markers now usedfor this-purpose. An anti-collision function is obtained by using a second series of pulses at the same airplane frequency together with a form o! direction iinder giving the approximate directions oi' any nearby airplanes. The latter transmission is modulated so as to indicate the altitude to nearby airplanes and likewise obtain the altitude indications of the nearby airplanes.

6. By means of a third series of pulses sent out at the same higher frequency from each airplane in reply to the signals from the rotary beacon, a quasi-radar service is provided on the ground which indicates the positions of all airplanes in respect to azimuth and distance more conveniently than is possible with ordinary radar equipment.

7. By modulating and keying this third series of pulses, the altitude and identity of each air- `plane is continuously indicated on the same f screen used for the quasi-radar indications. This automatic reporting thus provides continuously the information which is now obtained at intervals by oral communications from the pilots. Since these indications of altitude and identity are directly shown on the quasi-radar screen, there is no difculty in associating the altitudes and identities with the positions of the corresponding planes.

In accordance with the present invention, a radio system is provided in which all indications above listed may be given by means of a number of ground equipments employing only two major high frequencies, one for transmitting and one for receiving, and so synchronized that only one main U. H. F. receiver, one auxiliary U. H. F. receiver and one single U. H. F. transmitter is required on the airplane.

The above and other objects and features oi' our invention and the manner of attaining them are more fully explained in the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic view in perspective of three airports with associated airways; and Fig. 1A is an enlarged view of a part of the airway;

Fig. 2 is a plan view illustrating the general airport and radio range system;

Figs. 3 and 4, taken together, show circuit diagrams of the aircraft equipment for producing various indications;

Figs. 5 and 6, taken together, illustrate the transmitter installation at an airport, Fig. 5 showing the rotary beacon and distance repeater circuits, and Fig. 6 showing localizer and glide path beacon arrangements;

Fig. 7 is a diagram of the field patterns produced in the rotary beacon of Fig. 5;

Fig. 3 is a wiring diagram of a pulse width selector circuit used in the system;

Fig. 9 is a schematic diagram of the quasiradar indicator at the airport;

' Fig. 10 is a view of the sweep pattern of one of the oscilloscopes of Fig. 9;

Fig. 1I is a block diagram of the display and posting desk equipment at the airport;

Fig. 12 is a schematic diagram of the airways terminal eq/uipment showing the quasi-radar equipmentfor indicating the location of aircraft along the airways;

Fig. 13 is a schematic diagram of the terminal and relay equipment of the system showing in detail the communicating features thereof; and

Fig. 14 is a schematic diagram of the relay equipment used on the towers of the airways.

In Fig. l, there is shown in schematic form the layout of a typical airways system according to the principles of our invention providing comxnunicationA and quasi-radar facilities between airports i, 2. 3 and between airports and planes 4 and 5 over intermediate repeater or relay towers 8 which may be spaced along the airway, say,

every twenty miles. more or less. depending upon the terrain.A Each airport is provided with a. multichannel ultra high freuuencv transmitter adapted to send signals to other airports and to planes in flight by way of the repeater towers 8 (see Figs. 1A and 14) which are equipped with highly directional antennas providing for radiation in specied directions such as east and west, as well as upwards or for general broadcasting -in all directions. thus providing facilities for communication as well as range signals.

'I'he planes, in order to properly. cooperate with the traiiic-control system are provided with transmitting and receiving -eouipment adapted for ultra high frequency signalling and adapted to indicate their identity and altitude as described in more detail hereinafter.

The functions which must be performed to ,i provide for self-location are the determination on the plane of its own distance from the center of the airport and the determination on the plane of its azimuth angle as seen from the center of the airport. Both these functions require cooperation between equipment on the ground and equipment in the airplane. I'he following explanation of the principles of operation of the self-location service will be made in conjunction with Fig. 3 representing the self-position, beam reception and transmitter units of the airplane equipment and Figs. and 6 representing the airport equipment.

Turning to Fig. 5, basically 1| is a rotary beacon for sending out signals enabling a plane to determine its azimuth, while 12 is a self-distance repeater designed to receive certain types of pulses at a given frequency, F2 and to re-transmit them at a different frequency F1 for the purpose of enabling the plane to determine its distance from the center of the airport. In the airplane, Fig. 3,

repeater 12 through theself-position reception unit 13 to the indicator 14.

The'signals sent out from rotary beacon 1i, Fig. 5, for determining azimuth are of two kinds: rotary signals and reference signals. The rotary signals consist of a series of pairs of pulses of two different characteristics, for example, of 5 microsecond and 3 microsecond pulse widths transmitted, for example, 4000 times a second with two different directive patterns so chosen as to sharply dene an imaginary line hereafter called the sweep line. These diagrams are both rotated a given speed, for example at 12 times a second whereby the sweep line is correspondingly rotated. The reference signals merely consist 'of pulses of, for example, 12 microseconds width which are sent out uniformly in all directions at the instant when the sweep line is passing through true north. The latter reference pulse is only sent out every alternate time that the sweep line passes through north, so that this reference pulse is transmitted only 6 times per second. j

The pairs of pulses of 5 and 3 microseconds width are generated in double pulse generator 18 which is arranged to send out first a 5 microsecond pulse and then immediately thereafter a 3 microsecond pulse, such a pair of pulses being transmitted once every 250 microseconds. Both these pulses are applied to the same transmitter 11, operating at F1, but a switching circuit 18 which is timed by the pulse generator 18 routes the two types of pulses through different channels so that these can be radiated with dierent directive patterns. The 5 microsecond pulses pass out through the right hand side of switching circuit 18 to goniometer 85 which applies the signals variably to the four antennas 80, 8i, 82, 83 with such magnitudes and phases as to produce a figure of eight pattern 84 (see Fig. 7) having one oi its null directions aligned with the imaginary sweep line to be defined. The second null which is not desired but is inherent in this the unit 13 is primarily a receiver for receiving the azimuth signals from 1i while 14 is essentially an electromechanical unit for converting the received azimuth signals into mechanical rotation of oscilloscope sweep coil 8U.

The nature of these various equipments as well as their principles of operation can best be explained by tracing the progress of a set of azimuth signals through rotary beacon 1I and selfposition reception unit 13 to indicator 14, and by then separately tracing the progress of a selfdistance pulse from self-position reception unit 13 through transmitter 15 to the self-position repeater 12 as well as the progress of the retransmitted self-distance reply pulse from the type of pattern will be aimed to the rear (i. e., 180? away from the imaginary sweep line). The three microsecond pulses pass out of the left side of switching circuit 18 whence they are transmitted through goniometer 19 to the four antennas 80, 8i, 82, 83, and simultaneously throughl the normally closed cam switch 86 to the central antenna 81. The relative strengths of these signals is such as to produce a cardioid pattern (88 of Fig. '1); and the position of goniometer 19 is shifted 90 with respect to that of 85 so that the maximum of this cardioid willbe aligned with the imaginary sweep line while the null of the cardioid is aimed backwards in line with the undesired second null of the figure of eightpattern. By such an arrangement of the patterns, the imaginary sweep line is quite sharply defined since the line will be the only direction in lwhich a plane will receive pulses of 3 microseconds width without the reception of any pulses of 5 microseconds width.

The reference pulse of 12 microseconds width is generated by pulse generator 88A which is triggered for this purpose'by a switch geared down from the main motor I I5 so as to close 6 times per second when the sweep line is passing through true north. This 12 microsecond pulse is applied only tothe omni-directional antenna 81,v theswitch 88 serving to disconnect this antenna from the other antennas at this instant. The switch 88 also applied a ground to pulse generator 1.6, over lines 88, 90 at this same inl l stant, so as to temporarily lstop the transmission of the and 3 microsecond pulses, during the interval when the 12 microsecond pulse is to be transmitted and for about 12 milliseconds thereafter.

In the airplane equipment shown in Fig. 3, the various azimuth pulses are picked up by the an tenna of self-position unit "it and received by the receiver @l of this unit. The pulses delivered by the output of this receiver are separated by the width selectors @2, 33, tl.

The output of width selector 32 which passes only the 5 microsecond pulses is applied to bias the Width selector @l so as to block the latter for a given interval, say 25 microseconds. Therefore, the received pulses of 3 microsecond width are not able to -pass through width selector @il except when `these are received without any 5 microsecond pulse immediately preceding them. Thus, pulses of 3 microseconds Width will only be delivered from selector @di in brief groups 12 times a second when the imaginary sweep line of the rotating beacon swings past the airplane under consideration. The pulses thus delivered from 94 synchronize a lock-in oscillator 35 of a given periodicity, for example 12 periods per second; and the output of this oscillator 35 is passed through a phase splitter @t to the stator coils of goniometer t2, thus producing in this goniometer a magnetic i'leld rotating 12 times per second.

The 12 microsecond reference pulses which are sent out in all directions every second time that the imaginary sweep line passes through true north are similarly picked up by the antenna of reception unit 53, received in the receiver Si, and selected by width selector 33. From this width selector, the pulses pass to an unblocking circuit 9i over line 33a to momentarily unblock the associated discriminator circuit 98.

The rotatable (but normally stationary) search coil of goniometer t2 is continuously connected to the discriminator circuit 98 so that the alternating voltage produced in this search coil by the rotating eld above mentioned, is continuously applied to this discriminator circuit. In the normal blocked condition such alternating voltage produces no effect but when the discriminator 9@ is unblocked by the arrival of the 'l2 microsecond reference pulse, the polarity which the alternating voltage has at that instant will control the discriminator circuit so as to cause the latter to send out a positive or negative current for a short time e. g. 116 of a second). This brief surge of current passes through the motor tl thus tending to drive this motor clockwise or counterclockwise, with a corresponding rotation of the search coil of goniometer t2.

Assume that the relation between the time of receipt of the reference pulse and the time of receipt of the 3 microsecond pulses (without 5 microsecond pulses) is such that the goniometer search coil has a positive voltage at the instant of unblocking of this discriminator 98. Then at each unblocking of this discriminator circuit, a positive current will pass through motor 6i which will finally cause this motor to turn and rotate the goniometer search coil. This will continue until the goniometer search coil assumes a position such that the voltage which it delivers to the discriminator circuit 98 is zero at the instant of the unblocking of the discriminator circuit.

Thus, the action of the discriminator circuit 98 and motor tl is such as to rotate the goniometer search coil to a given position dependent upon the time of receipt of the reference pulse with respect to the instant when the imaginary sweep line of rotary beacon swings past the airplanes. 'I'his will mean that the goniometer searchcoil will always assume a position corresponding to the azimuth angle of the airplane as seen from the rotary beacon 1i.

In addition to, the azimuth angle, it is also necessary to obtain an indication of the airplanes distance from the center of the airport,

in order that the complete position of the airplane can be shown on a map of the airport. Such an indication is obtained by triggering transmitter @il by pulses from pulse generator it@ to cause it to transmit at its carrier frequency of F2 a self-distance pulse of a given character, for example. of 1/2 microsecond width to the self-distance repeater l2 at the airport (Fig. 5). The self-distance repeater then re-transmits a corresponding self-distance reply pulse also of l/g microsecond width but on a dinerent carrier of F1 frequency. The self-distance reply pulse is then received in 9i and the distance of the airplane from the ground is determined by using this reply pulsey to illuminate a spot on the screen of self-position oscilloscope 59 whose deilection plates are fed from a sweep circuit itl synchronized with the transmission of the outgoing selfdistance pulse from generator lim.

Considering these operations in greater detail, the self-distance pulse originates in non-synchronous generator im) which generates a pulse of 1A microsecond width approximately 30 times per second. 'I'he pulses from in@ are applied through limiter 02 in the transmitter unit l5 to the F2 transmitter 99 which thereupon radiates a corresponding half microsecond pulse of F2 carrier to the self-distance repeater i2 at the airport. This self-distance repeater receives the self-distance pulses on antenna ID3 and retransmits a pulse of the same width but on a different carrier frecuency F1 from antenna 104, this pulse being referred to as a self-distance reply pulse.

The reply pulse from repeater 'l2 is picked up by the antenna of self-position reception unit 13, received in receiver 9i and selected by width `se lector Q05. From the output of MI5 the pulse is applied to a control grid |06 of oscilloscope 59 in the self-position oscilloscope unit 14. At the instant when the pulse was applied from the pulse generator IM to the transmitter unit 15, this same pulse was also applied to blanked sweep circuit ini to initiate the sweeping action of this circuit. 'I'he sawtooth sweep voltage thus produced is applied to sweep coil 6D which magnetically controis the beam deiiection of oscilloscope 59. Accordingly. when the self-distance reply pulse is applied to the grid of this tube, as previously described the visible spot thus produced has a radial deflection corresponding to the time interval between the sending of the .self-distance pulse and the reception of the self-distance reply pulse. Thus, the radial deection of this spot measured from the center of the oscilloscope'accurately represents the distance of the airplane from the center of the airport.

'Ihe direction in which the spot is radially deected outward from the center of the circle, depends upon the rotary position of the sweep coil 60. This coil, however, is supported by the shaft of the goniometer 62 so that its position corresponds to the position of the search coil of this goniometer. As was previously explained in connection with the description of the transmission and reception of azimuth signals, the Search i3 coil of this goniometer l2 is controlled so as to constantly assume a position corresponding to the azimuth angle of the airplane as seen from the beacon 1| at the center of the airport. Thus, the

luminous spot appearing on the screen of the oscilloscope 59 will have a position which corre- 'sponds both in distance and azimuth to the position of the airplane with respect to the center of the airport.

LANDING BEACNS AND RANGE SERVICE The functions to be performed in orderto render the landing beam and range service are essentially the functions generally performed separately by arnumber of glide paths, localizers and ranges on'the'ground cooperating with separate glide path receivers, localizer receivers and range receivers in the air. In accordance with the present invention, all these services are rendered simultaneously on one single carrier frequency which is also the same frequency used forthe self-location services.

These functions will now be described in connection with Figs.' 3 and 6. The usual 90 and 150 tone frequencies may be replaced by high frequency tones of the order of hundreds of kilocycles and these different frequencies or tones are used for the different glide path and localizer equipments. As an example, a system having the runway A, B and C 4and four range beacons called D. E, F and G may be considered. Twenty such tones are, therefore, required, the lowest four tones being used for the "A glide path and localizar combination. the next four for the "B" glide path and localizer combination and the third group of four for the C combination of glide path and localizer. The last eight tone frequencies are allotted in pairs tothe ranges D, E, F and G.

A suitable set of twenty tones is as 718 and 650 kc. for "A glide path 838 and 770 kc. for B glide path 958 and 890 kc. for "C" glide path 742 and 6'14 kc. for A localizer 862 and '794 kc. for B" localizer 982 and 914 kc. for localizer 1078 and 1010 kc. for D range 1102 and 1034 kc. for "E range 1.198 and 1130 kc. for "F range 1222 and 1154 kc. for G range It will be noted the above listed frequencies have been selected according to a systematic plan so that the lowest four frequencies. when mixed with a heterodvning oscillation of '702 kc; and then demodulated will yield beat frequencies of 16. 28 40 and 52 kc. respectivelv. 'I'he next four tone frequencies. when mixed with a heterodvning oscillations of 822 kc. and then demodulated will also vield the same values of beat frequencies (18. 28, 40 and 52 kc.) while the third group of four tones when heterodyned with 942 kc.. or the fourth group of four tones when heterodyned with 1062 kc., or the fifth group of four tones when heterodyned with 1182 kc. will also yield the same four beat frequencies. This relationship between the tone frequencies simplifies the design of the receiver which need only have four fixed lters for passing 15. 28, 40 and 52 kc. respectively, and five crystals for providingheterodyning frequencies of 702. 822. 942, 1062 and 1182 kc.

In order to still further reduce the possibility of interference between the various glide path, localizar and range transmitters, the several transmissions from these transmitters take place follows intermittently at rapid rate, for example, six times per second, nd definite time intervals are assigned to each ,transmission so that no two transmissions will take place simultaneously. Also, each transmitter sends its own two transmissions successively. In other words, in lthe case of a glide path transmitter, the y up and ily down" signals are successively transmitted, similarly in the case of a localizer or range the ily let and y right signals are successively trans tted. Accordingly, ten different pairs of time intervals are required for the simultaneous operation of three glide paths, three localizers and four ranges.

In order to carry out the above mentioned two principles of timing the transmissions of the different glide paths and localizers so as to occur successively and adjusting their modulationsfrequencles so as to be diiIerent-from one another, the ground equipment required for the landing beam and range service includes not only the glide path, localizer and range transmitters themselves. but also a central landing beam control equipment" which is shown in Fig. 6.

Fig. 6 showsy essentially control equipment |09, together witha number of localizers I i0 and a number of glide path beacons Il I. .A number of range beacons are also provided connected to leads I2 but are not shown and need not be considered in detail since they .may be of any conventional form.

If more runways are provided a correspondingly` when the transmission of the 5 and 3 microsecond pulses normally sent out by the rotary beacon 1| is temporarily silenced by switch 86 of such beacon. Each of these groups of synchronizing impulses produced by the keyer ||3 consists of 10 triggering impulses of any convenient length transmitted successively one microsecond apart over the 10 yseparate output circuits H8, H9, |20, |2|, |22, |23, |21, |25, |28. Each of these 10 output circuits is preferably provided with a corresponding delay adjustment by means of circuit |21| 3B so that the relative timing of the synchronizing pulses received over these 10 outputs can be accurately adjusted.

The last four of the 10 output circuits are used for synchronizing the range transmissions which are located away from the airnort and the corresponding outputs |23, |24, |25, |26 of ||3 are, therefore, connected to the airways terminal equipment over lines ||2. The first six sets of synchronizing pulses in each group are used to synchronize the transmissions of 3 of the localizers and 3 of the-glide paths.

In the simple three runway system only one glide .l path and one loca1izer beacon would normally be operative. At a larger airport more runways may be available for simultaneous use. It is considered, however, that not more than 3 glide paths and 3 localizers will be operated at any one time. The selection of which 3 localizers and glide paths are to be used at any given time will be principally governed by the direction or velocity of the wind which may change within a comparatively short interval. lt is desirable to provide for changing selection of these beacons quickly and conveniently. Accordingly. a group of 6 switches |8i|92 is provided, which are ganged to-be operated by one single manual control |99, and the connections from the first 6 output circuits |27, |28, |29, |99, 53|, |32 of master keyer ||3 to the selected 3 glide path beacons and 3 localizer beacons are controlled by these switches. Thesix glide path beacons are designated by Bild-|98 respectively and the six localizers by MiB-|55 respectively.

. If the ganged switches itl-|132 were set to their first position with their wipers resting on their number i contacts, the first 3 output circuits H8, i9 will be routed to glide paths |96, |65 and |98 respectively, 'while the next 3 outputs |29, |2| and |22 will be routed to localizers |59, and |52. Thus. localizer |59 and glide path |59 will be made eiiective to define a rst landing beam;l localizer |5| and glide path |95, would be eective for a second landing beam: and -localizer |52 and glide path |439 will be effective for a third beam. Similarly, if the switches were set to their second position the iirst beam will be defined by localizer |5| and glide path |95, the second beam by localizer |52 and glide path |95, and the third beam by localizer |53 and glide path |657. In corresponding manner. other switch positions will render other combinations of glide path and localizer beams effective.

lin order to render a given glide path or localizer effective for defining a certain beam, such glide path or localizer must not only receive the appropriate synchronizing signal from master keyer ill] so as to cause it to perform its transmissions during the two appropriate intervals allocated to that beam, but must also receive an additional controlling signal to cause it to employ the appropriate modulation tones allocated to that beam. Thus, a localizer which is to operate on the third beam must not onlv receive a synchronizing pulse from output |22 which defines the time for localizer transmissions from the third beam but must also be controlled to employ modulation tones of 914'.` and 982 kc. which are the tones allocated for localizer transmission on this beam. (See the table of tone frequencies given above.)

The control necessary to cause the selection of the appropriate tone frequencies in the several localizer and glide path equipments may consist of three distinctive signals of any type (e. g. +D. C., -D. C. and 60 cycles A. 0.). These three characteristic frequencies may be directly superposed on the synchronizing pulses being thus controlled through the same switches 137-142 which control these impulses. Accordingly, it maybe assumed that tone selector signal source |56 applies to outputs and |29 of master keyer H8, a positive D. C. superposed upon the previously mentioned synchronizing pulses, while outputs I8 and |2| have negative D. C. and outputs ||9 and 2| have low frequency alternating current superposed upon their synchronizing pulses. These combined pulses operate at the glide path and localizer systems to select the desired combinations of tone" frequencies in any convenient known manner.

Up to this point only the landing beam control equipment has been considered in detail. It is believed that no similar detailed description of the glide path or localizer transmitters themselves nor of the receiving and displaying equipments on the airplane is necessary.

Just prior to the reception of the various ily left and "fly right signals in the three operative localizers and of the corresponding' fly up and "ily down signals of the three glide paths, the airplane will receive a l2 microsecond pulse of F1 carrier frequency from the rotary beacon 7| as previously explained in the description of the self-location service. Such signal in addition to being applied to unblocking circuit 9i as previouslv described, is simultaneously'applied to unblocking circuit |85 of beam reception unit |5'|, thus preparingthe unit |57 for the subsequent reception of the various fly down, fiy left, "ily right signals.

When the fly left signal arrives from localizer |89l which is assumed to be conditioned for, dening the B beam, as above described, this signal will be received in receiver 9| thus yielding a rounded train of 862 kc. waves. Such train of waves will be applied not only to the width selectors 92, 98, 99 (which will not respond to this signal) but also through unblocking circuit |85 to the mixer |86 of unit |51?. Assuming that switches |87, |88, |89 have been set to their second position as shown, so as to condition this beam reception unit B for receiving the signals of the B beam, the oscillator |99 will be generating a frequency of 822 kc. which will be constantly applied to the mixer |88. The 862 kc. tone from the "fly left signal when rnixed with this 822 kc. heterodyning'wave will yield in the output of mixer |86 a 40 kc. beat note which will pass through the lter |9| to varistor |92. This varistor |92 will rectify the signal to produce a positive current which will pass through switch |88 in its second position to the meter movement |83 of display unit |58.

zov

When the immediately succeeding iiv right signal arrives at the airplane, it is similarlv received ln receiver 9| to yield a 794 kc. tone which is applied through unblocked circuit to the mixer |86 as before. Such 794 kc. tone when heterodvned with the 822 kc. output from |99 will yield a beat note of 28 kc. which will pass through the filter |94 to the varistor |92. The polarity of the connections from |94 to |92 should be such that the current produced by rectification of |92 will be negative. This negative current will again be applied through switch |88 in its second position ,to the meter movement |99 of display unit |58.

Assuming that the plane is exactly on course so that the ily right and "fiy left signals are received with equal amplitudes, the positive and negative currents which will be applied to the meter movement |93, as above explained, will be of the same magnitude and, therefore, no deflection will be produced. If, however, the plane is to the left of the course, the fly right signal will be predominantly received so that the negative current will exceed the positive current, thus resulting in a deflection. of the pointer |95 of |83. If the plane is to the right of the course the pointer will be deflected in similar manner but in the opposite direction.

Immediately before the receipt of the two signals above traced-i. e. the "fly left and the fly right signals from the localizer used for the B beam, the plane will receive a corresponding pair of y up and fly down signals from the glide 17 path used for the B beam; rIn the case assumed, where localizer |50 is used for the B beam. the glide path used for this same beam would be glide path |44.

The description of the reception of localizer signals may be considered as applicable also to the glide path, since all glide path and localizer equipments may be essentially identical. In fact, the only difference between the glide paths and localizers is a diierencein the antenna arrays employed and a dierence in the frequencies of the transformers, and of the three modulating frequencies.

The localizer signals will control meter movement |93 of display unit |58, Fig. 3, while the glide path signals will correspondingly control meter movement |99 of this unit. Meter movement |99 carries a luminous ring 200 which is deflected back and forth (so that its image as seen in inclined mirror 20| seems to move upward or downward) under control of the glide path signals. Meter movement |93 carries a luminous spot 202 normally positioned centrally behind the luminous ring 200 but capable of moving right or left under control of the localizer. The relative positions of the spot and ring are thus controlled by the landing beam signals to produce the several different types of indication.

The inclined mirror 20| is controlled by Selsyn motor 202 (which is actuated from the radio compass unit) and by a gyroscope 203, having its axis of rotation vertical. Accordingly, the mirror will be tilted vertically by the gyro in response to a vertical tilting of the plane and will be tilted left or right by the radio compass when the plane turns right or left. The luminous spot and ring carried by the meter movements |93 and |99 will, therefore, appear to shift with respect to the viewing frame in the desired manner.

The horizon bar 204 is tilted by sideways tilts of the gyro 203 to show the angle of bank. This bar is placed behind the mirror 20| at the position of the virtual image of the spot and the mirror is sufiiciently transparent so that this bar can be seen.

RADIO COMPASS FEATURE localizer or range signals are made use of. The

airplane equipment for performing the radio compass function consists of a forward scanning radio compass unit 205 with a suitable antenna array 206 fixed on a forward portion of the airplane, and a bearing indicator 32 (see Fig. 3). The self-position reception unit 13 and the beam reception unit |51 which have already been described as used for other functions are also employed for the radio compass function.

The radio compass unit 205, Fig. 3, essentially includes a pattern shifting means 201, 208, an electronic reverser 209, a rotary mechanism motor 2|0 and a modulation detection circuit.

18 The energy received on antenna array 206, after passing through phase shifters 201, 208 and electronic reverser 209 is applied over line 2|| to the input of receiver 9|. This energy is applied over unblocking circuit |86, mixer |66 and filter 2|3 to a modulation detector 2|4. Filter 2|3 is tuned to pass the beat frequency corresponding to the localizer signal. This energy will carry a modulation dependent. upon the antenna switching action in antenna array 206. Modulation detector 2|4 detects only this modulation produced by the reversing switching of electronic reverser 209. When array 206 is aligned with the localizer transmitter, the two outer antennas which are coupled in phase opposition due to transposition 2|5 will have no effect. The electronic reverser 209 serves alternately to connect the central antenna of the array 206 with one, and the other the two outer antennas, thus producing a modulation effect whenever the outer antennas are not arranged for null reception. This modulation effect, detected in 2|4, serves tol control `reversible motor 2|0 in accordance with the phase of departure of the null reception with respect to the center antenna.

If the antenna is not aligned with the localizar beacon, the incoming signals applied to modulation detector 2| 4 over filter 2|3 will produce a resultant current which will drive motor 2|0 in one direction, The shaft of motor 2|0 is coupled over reduction gearing 2|6 to phase shifters 201 and 208. These phase Shifters are arranged to `adjust the phase of the two outer antennas so that the null of the two outer antenna units will be readjusted into alignment with the transmitting beacon. Accordingly, these antennas will again be quickly aligned to null position.

Also coupled to th shaft of motor 2|0 is a Selsyn generator 2|1. Selsyn generator 2| 1 is connected by line 2|8 with Selsyn motor 202a to control the position of mirror 20|. Selsyn generator 2|1 is also further connected to a second Selsyn motor 2|9 which controls pointer 220 on bearing indicator 32.

PULSE WIDTH SELECTOR 'I'he pulse width selectors, shown in the various parts of thesystem, may be of any desirable type. These width selectors serve to select pulses of any particular width to the exclusion of other pulses. In Fig. B is illustrated a simple form of width selector described in detail in the copending application of E. 4Labin and D. D. Grieg, Serial No. 487,072, filed May 15, 1943, now Patent No. 2,440,278 issued April 27, 1948.

The pulses are applied to a tube 22| and produce in the output thereof negative pulses shown at 222. These negative pulses are applied to shock excite tuned circuit 223 which is tuned to a frequency of which the pulse width represents one-half a wavelength. The pulses are simultaneously applied to the grid of damping tube 224 connected across tuned circuit 223. The pulses applied to circuit 223 will produce a wave having a negative portion, as shown at 225, and a positive portion at 226. The oscillations produced in circuit 223 will tend to go negative after portion 226 has been produced. However, damping tube 224 will short-circuit any further negative portion since, at this time, the negative pulse 222 no longer is present on the grid of tube 224. As a consequence, only the portions 225 and 226 are produced.

If pulses of different widths, either smaller or larger, are applied to the input circuit, these 

